1. Field of the Invention
The present invention relates to a centralized supervisory system, and more particularly to a remote supervisory system that can reduce a time delay occurring at a master station (the central station) in detecting alarms from slave stations (the stations supervised by the master station).
2. Description of the Related Art
Usually, in a communications network, slave stations are provided which supervise network elements, such as transmitting equipment, that form part of the communications network, and a master station having the facilities for remotely supervising the slave stations is provided, thus implementing a remote supervisory system for remotely supervising the network elements at the master station.
Generally, in this type of remote supervisory system, a polling selection system is employed. In polling, master supervisory equipment (M-SV) responsible for centralized supervision transmits a polling signal (a send request signal) to slave supervisory equipment (S-SV) provided for network elements (NEs), in response to which signal the S-SV reports the current conditions of the NEs to the M-SV. The polling signal is sent out at fixed time intervals; the signal can also be sent out at any desired time when a maintenance person makes a request by designating a specific NE or all the NEs. This polling system has the advantage that the condition of any specific NE or all the NEs can be checked at any time since the maintenance person can transmit a send request at any desired time. On the other hand, the disadvantage of this system is that there is a time lag between the occurrence of an alarm and the detection of that alarm because a fault condition (alarm) occurring at a certain NE cannot be detected by the M-SV unless the M-SV issues a send request to the S-SV that supervises the NE that is causing the alarm.
On the other hand, an instantaneous alarm transmit system is known whereby an alarm is sent to the M-SV upon the occurrence of an alarm condition. With this system, an alarm can be detected without delay, but the drawback is that the M-SV cannot issue a send request to the S-SV.